Internal combustion engine having high performance combustion chamber

ABSTRACT

An internal combustion engine has a cylinder head with a combustion chamber defined by a depression in the head. The raised face surface of a piston extends into the combustion chamber in the cylinder head as the piston approaches top dead center, and creates turbulent squish currents within the chamber as closely matching surfaces on the piston face and on the walls of the combustion chamber in the head force gases out from between these surfaces. The turbulence helps to prevent autoignition and allows higher compression ratios than would otherwise be possible.

FIELD OF THE INVENTION

The present invention relates generally to internal combustion engines,and more specifically to carbureted spark-ignition internal combustionengines with high compression ratios.

BACKGROUND OF THE INVENTION

In carbureted spark-ignition engines, one means of increasing thethermal efficiency (and thus the work output) of the engine is toincrease the compression ratio, defined as the ratio of the maximumvolume between the piston and the head to the minimum volume between thepiston and the head. A higher compression ratio increases the thermalefficiency of the engine. It is therefore desirable for high-performanceengines to have the greatest compression ratio possible.

However, the compression ratio cannot be increased indefinitely. Thehigher compression ratio causes higher temperatures and pressures in thecombustion chamber's fuel-air mixture upon compression, therebyincreasing the possibility of rapid self-ignition of the fuel-airmixture at some unplanned point during the work cycle. Such an event iscommonly referred to as "knock" or autoignition.

A high degree of autoignition is undesirable because it lowers theengine efficiency and it also increases the chances of engine failure.Engine efficiency drops when autoignition occurs because cylinder gasexpansion occurs at a time when its work potential cannot be fullyutilized. For maximum work output, ignition is best begun shortly beforethe piston reaches top dead center so that peak combustion chamberpressures occur shortly after the piston reaches top dead center. Peakpressures at this point allow the work generated by the expandingcombustion gases to be utilized over the greatest length of pistontravel. The rapid pressure increases associated with autoignition cancause peak pressures to occur before this point, perhaps when the pistonhas not yet reached top dead center, thereby causing work losses byopposing the piston motion. Further, autoignition promotes heat lossesfrom the engine because the combustion gases vibrate and "scrub" thecylinder walls as the shock wave from autoignition travels through thecylinder. Autoignition can also cause premature engine failure due tothe extremely high temperatures it causes in the cylinder, as well asfrom the damage it causes by stress from the shock waves.

Autoignition is frequently triggered in high compression ratio enginesby the normal process of ignition. The spark plug (or plugs) ignites thecompressed fuel-air mixture, and as the flame front begins to travelfrom the spark site through the chamber, the end gas--the fuel-airmixture in the cylinder farthest away from the spark plug(s)--isadditionally compressed by the expansion of the gases behind the flamefront. The mixture is already at a state of high temperature andpressure due to its previous compression, and if this additionalcompression of the end gas causes further temperature and pressureincreases, the end gas may autoignite.

While autoignition may be decreased by using a fuel with a higher octanerating--and therefore a higher ignition temperature--it is also helpfulto increase the speed of combustion, leaving little time forautoignition of the end gas to occur. A number of steps may be taken toincrease the rate of combustion, such as the use of modified fuels ormultiple spark plugs. Another method involves increasing the turbulencein the combustion chamber immediately prior to and during combustion.Turbulence within the chamber causes the uniform flame front within thecombustion chamber to distort, creating a more convective mode of heattransfer and sending "tongues" of highly reactive radicals from theflame front into the unburned mixture. These conditions combine topromote more rapid combustion of the unburned mixture than would occurin a quiescent, low-turbulence mixture.

While some turbulence is created within the combustion chamber by themere act of the piston compressing the air-fuel mixture, the effect canbe heightened by modifying the shape of the combustion chamber so thatthe motion of the piston interacts with the chamber contours to causegreater turbulence during compression. It is especially desirable if thegreatest turbulence occurs in the end gas near the end of thecompression stroke, just before ignition. Examples of chamberconfigurations designed to promote mixing and/or turbulence are found inU.S. Patents 4,838,222, 4,844,040, 5,115,774, and 5,115,776.

It is further desirable for the combustion period to be approximatelyconstant, when measured in crankshaft degrees, over the range of speedsat which the engine will operate. This insures that regardless of enginespeed, the expanding combustion gases will exert their peak pressureswhen the piston is at approximately the same position. A constantcombustion period further insures that as the engine speed increases,thereby decreasing the compression time and causing more rapidtemperature and pressure increases, the time for autoignition to occurwill be proportionately decreased. A near-constant combustion period canbe accomplished if the combustion chamber can be designed so thatturbulence increases as engine speed is increased.

Autoignition is present in almost all internal combustion engines tosome extent, and is difficult to totally eliminate. The goal ofhigh-performance engine design is to minimize autoignition to such anextent that it no longer harms the engine's performance or itsstructure, while at the same time obtaining the highest compressionratio possible.

SUMMARY OF THE INVENTION

The internal combustion engine of the present invention operates with ahigh compression ratio while allowing the use of standard fuel. Morespecifically, the invention provides a carbureted spark-ignition engineparticularly suited for motorcycles, with a high compression ratio, forexample, on the order of 83/4:1 to 17:1, which may operate on standardfuel without undue autoignition. The invention is able to attain thisincreased compression ratio by heightening the turbulence in the endgas. Further, autoignition is minimized at all operating states of theengine by increasing the turbulence in the end gas as the engine speedis increased so that the combustion period is approximately constant,when measured in crankshaft degrees, at all engine operating states. Inthis manner, the engine is able to achieve superior power output at allspeeds without the damage and inefficiency associated with autoignition.Further, since the increased turbulence in the combustion chamberenhances combustion throughout the chamber, more complete combustion isobtained, leading to an increase in fuel economy and a reduction in theemission of unburnt hydrocarbons.

An engine assembly in accordance with the invention includes a cylinderhead, a cylinder block, and a piston (or pistons) which reciprocates ina cylinder within the block. The cylinder head and block are attached toeach other at a cylinder head mating surface and a cylinder , blockmating surface. The cylinder head includes an inlet valve and inletport, an exhaust valve and an exhaust port, a cylinder head combustionchamber, and the cylinder head mating surface. The shape of cylinderhead portion of the combustion chamber is defined by a recess in thecylinder head mating surface extending towards the interior of thecylinder head. The recess includes a depression which is bounded at itsperiphery in part by a chamber shoulder, and this chamber shoulder is inturn bounded by a beveled rim surface extending from the periphery ofthe chamber shoulder to the cylinder head mating surface. The wall ofthe depression includes an inlet valve seat, an exhaust valve seat, anda spark plug seat in which a spark plug is mounted. When the inlet andexhaust valves are closed, their heads rest in their respective inletand exhaust valve seats and form a barrier between the combustionchamber and the inlet and exhaust ports. The inlet valve seat andexhaust valve seat may extend beyond the periphery of the depression,thereby overlapping the chamber shoulder and/or the beveled rim surfaceand interrupting one or both of them. Thus, the chamber shoulder andbeveled rim surface may exist in discrete segments which are interruptedby the valve seats, rather than continuously extending around the entireperiphery of the depression.

In a preferred embodiment of the invention, the depression has asubstantially semiovoidal surface, shaped similarly to an ellipsoidwhich is cut at a plane parallel to its major axis of rotation. Theinlet and exhaust valve seats sit on opposite ends of the major axis atpositions near the cylinder head mating surface and extend into thedepression. The exhaust valve is preferably somewhat smaller than theintake valve. The ignition means, e.g., a single spark plug, is locatedon one side of the major axis between the valve seats. The chambershoulder and the beveled rim surface preferably do not extend around theentire perimeter of the depression. They instead exist in two segments,each segment laying opposite to one another between the inlet andexhaust valve seats. While the segments extend so far as to end at theperiphery of the intake valve seat at one side of the combustionchamber, they do not extend to the periphery of the smaller exhaustvalve seat at the other side of the combustion chamber, and the surfaceof the depression surrounds much of the exhaust valve seat. Further,while the surface of the depression is substantially semiovoidal andthus has an oval periphery, the segments of the beveled rim surface donot conform to the arc of the oval periphery on either side of the majoraxis; the beveled rim surface exists as a straight planar segmentextending from the region near the exhaust valve up to a point near theminor axis of the oval periphery, at which point it then curves towardsthe inlet valve.

The block of the engine includes a cylinder (or plural cylinders), apiston which reciprocates within the cylinder, and the cylinder blockmating surface. The piston has a piston top face which includes a pistonface reference surface and a raised piston face surface. When the pistonis at top dead center, the piston face reference surface liessubstantially in the plane of the block mating surface. The raisedpiston face extends above the plane of the piston face reference surfaceand comprises a beveled boundary surface, a raised planar face surface,and optionally a beveled valve clearance surface. The raised planar facesurface is spaced above the piston face reference surface and is boundedby the beveled boundary surface, which extends from the raised facesurface to the piston face reference surface. Therefore, when the pistonis at top dead center, the raised planar face surface extends beyond thecylinder block mating surface and into the combustion chamber. At thispoint, a peripheral portion of the raised planar face surface closelyapproaches and is parallel to the chamber shoulder, and the beveledboundary surface closely approaches and is parallel to the beveled rimsurface. This close approach of these surfaces produces strong currentsin the combustion chamber as the piston approaches top dead center, bydriving the fuel-air mixture from between these parallel surfaces intothe combustion chamber. Additional squish currents are generated as thepiston face reference surface closely approaches the portion of thecylinder head mating surface immediately adjacent to the combustionchamber.

If a portion of the chamber shoulder is wider than at other positions onthe chamber shoulder, the piston will push a greater volume of gas fromthe space between this larger shoulder area and the raised pistonsurface than from other positions on the shoulder. The squish currentgenerated at this point will therefore have greater velocity than at theother points, and greater turbulence will be induced in the area of thecombustion chamber opposite this point. In the preferred embodiment ofthe invention, a larger shoulder is used opposite the spark plug togenerate greater turbulence across the combustion chamber toward thespark plug immediately prior to and during ignition to assist in a morerapid and uniform ignition of the fuel-air mixture in the chamber.

The valve seats within the combustion chamber may extend beyond theperiphery of the depression and onto the chamber shoulder and/or thebeveled rim surface. To avoid having portions of the raised piston facestrike the valve heads when the piston approaches top dead center,beveled valve clearance surfaces are provided on the raised piston face.These surfaces are recessed from the raised piston face so that thepiston does not collide with the valve heads when the piston reaches topdead center. The beveled valve clearance surfaces are shaped such thatthey closely approach and are substantially parallel to the valve headsat top dead center, thereby producing additional squish currents bydriving the fuel-air mixture from between these surfaces and the valveheads and into the main volume of the combustion chamber.

The engine of the invention is particularly suited for use inmotorcycles. Depending on the performance requirements for the engine,the compression ratio of the engine may be reduced by forming adepression in the center of the piston face, thereby lowering thecompression ratio and allowing the use of lower octane fuels, andallowing greater flexibility for use of head and piston kit withdifferent displacement engines. The entire engine may be installedwithin a motorcycle as a unit, or the cylinder head or piston may beinstalled within a motorcycle engine of similar and compatible type. Thecylinder head and piston may be provided as a kit so that it will bepossible to install both the cylinder head and piston in existingmotorcycle engines.

Further objects, features, and advantages of the invention will beapparent from the following detailed description when taken inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a cross-sectional view of a portion of an engine in accordancewith the present invention, showing the cylinder head assembly, thecylinder block, and the piston.

FIG. 2 is a cross-sectional view of the engine of FIG. 1 when the pistonis at top dead center.

FIG. 3 is a cross-sectional view of the engine of FIG. 2, when thepiston is at top dead center, viewed at a point 90 degrees around theaxis of the cylinder from FIG. 2 and generally along the lines 3--3 ofFIG. 2.

FIG. 4 is a schematic view of the approximate volume defined by thecombustion chamber of FIG. 3.

FIG. 5 is a schematic view of the approximate volume of the combustionchamber showing the additional chamber volume of the depression when amodified piston, with a depression in the piston top face, is used.

FIG. 6 is a plan view of the cylinder head, showing the inner walls ofthe combustion chamber within the cylinder head.

FIG. 7 is a plan view of the piston showing its top face.

FIG. 8 is a perspective view of the piston of FIG. 7.

FIG. 9 is a plan view of a piston modified by the formation of adepression on the piston top face.

FIG. 10 is a perspective view of the modified piston of FIG. 9.

DETAILED DESCRIPTION OF THE INVENTION

With reference to the drawings, a cross-sectional view of a carburetedspark-ignition internal combustion engine assembly in accordance withthe invention is shown in FIG. 1. The engine assembly includes acylinder head 10 which is mounted atop a cylinder block 12. The headincludes an intake valve 14, an intake valve guide 16, an intake port18, an exhaust valve 20, an exhaust valve guide 22, and an exhaust port24. Within the cylinder head 10, a combustion chamber 26 is formed whichincludes a beveled rim surface 28, a planar chamber shoulder 30,composed of separated portions 30A and 30B, as shown in FIG. 3, andwalls defining a depression 32. Other views of the cylinder head 10 areshown in FIGS. 3 and 6, with a cross-sectional view in FIG. 3 and a planview in FIG. 6; these will shortly be discussed in greater length. Thecylinder block 12 has a cylinder defined by a cylindrical wall 33,within which a piston 34 reciprocates. The piston 34 pivots about anwrist pin 36 which attaches the piston to a connecting rod 38. A pistontop face 40 includes a piston face reference surface 42, and a raisedpiston face 44 which includes a beveled boundary surface 46, beveledvalve clearance surfaces 48, and a raised planar face surface 50. Theview shown in FIG. 1 is of the engine as it undergoes its intake stroke,indicated by the head 51 of the intake valve 14 clearing an intake valveseat 52. At this point, the head 53 of the exhaust valve 20 is nestedwithin an exhaust valve seat 54. As illustrated in FIGS. 1 and 2, aplanar cylinder head mating surface 58 is mounted in adjoining relationto a cylinder block mating surface 56 with a head gasket 59 between thetwo surfaces. For clarity of illustration, other standard parts of theengine (e.g., the crankshaft, valve lifters, camshaft, push rods, etc.)are not shown in FIGS. 1 and 2, and any suitable parts may be used. Theengine (e.g., an air cooled motorcycle engine) may also have two or morecylinders constructed as described.

FIG. 2 shows a cross-sectional view of the engine assembly as in FIG. 1but at the point when the piston 34 is at top dead center. FIG. 3 showsa cross-section of the engine of FIGS. 1 and 2 along a section linerotated 90 degrees around the cylinder axis from FIGS. 1 and 2. At topdead center, the raised piston face 44 extends beyond the mating surface56 of the cylinder block 12 and into the combustion chamber of thecylinder head 10. The beveled boundary surface 46 of the piston closelyapproaches and is parallel to the beveled rim surface 28 in the cylinderhead 10. Similarly, edge portions of the raised planar face surface 50closely approach the chamber shoulders 30A and 30B in the cylinder head,and edge portions of the piston face reference surface 42 closelyapproach the cylinder head mating surface 58. A squish current isgenerated when the fuel-air mixture between the approaching surfaces 46and 28, 50 and 30A and 30B, and 42 and 58, is rapidly compressed as thepiston 34 approaches top dead center, and the fuel-air mixture betweenthese surfaces is driven at high velocity into the combustion chamber26. The beveled valve clearance surfaces 48 (as shown as hidden lines inFIGS. 1 and 2) allow the piston 34 to clear the heads 51 and 53 ofvalves 14 and 20, respectively, when the piston is at top dead center,allowing the piston to reach a position closely adjacent to the valveheads and thereby producing additional squish currents.

FIG. 4 is an idealized schematic side view of the approximate volumedefined by the combustion chamber at top dead center. In the preferredembodiment, the cylinder head combustion chamber has a volume 70 whichis much greater than the main "squish volume" 72 (the volume definedbetween the raised piston face surface 50 and the chamber shoulders 30Aand 30B) and between the beveled boundary surface 46 and the beveled rimsurface 28. For example, if the combustion chamber 70 has a volume of112.5 cubic centimeters (cc), then the squish volume 72 may have avolume of, for example, 12.9 cc. FIG. 5 illustrates the volume definedby the combustion chamber at top dead center with a modified pistonhaving a depression in the piston top face 40 which adds a volume 74(of, for example, 43.1 cc), to the combustion chamber 26 to reduce theoverall compression ratio.

FIG. 6 is a view of the cylinder head 10 showing the combustion chamber26 and the cylinder head mating surface 58. As shown therein and in FIG.1, the intake valve 14 and intake valve seat 52, exhaust valve 20 andexhaust valve seat 54, and a spark plug 80 are all mounted on thedepression wall 32 which defines part of the combustion chamber in thehead. The depression wall 32 is bounded on two sides by the chambershoulders 30A and 30B, which are in turn bounded by the beveled rimsurfaces 28. The chamber shoulder 30A, at a position opposite the sparkplug 80, is preferably wider than the chamber shoulder 30B on the sameside of the combustion chamber 26 as the spark plug 80. The widerchamber shoulder 30A causes a greater volume of fuel-air mixture to bedriven away from the approaching surfaces at the area of the shoulder30A as the piston 34 approaches top dead center than from the area ofthe chamber shoulder 30B, thereby creating a higher-velocity squishcurrent and more turbulence which extends across the combustion chamberto the vicinity of the spark plug 80. Since ignition occurs shortlybefore the piston 34 reaches top dead center, the especially turbulentconditions near the spark plug 80 during ignition help the flame front,which is advancing outward from the spark plug 80, to distort and spreadrapidly through the combustion chamber 26.

The depression 32 defining the combustion chamber has a substantiallysemiovoidal shape (a portion of an ellipsoid), with the heads of theintake valve 14 and the exhaust valve 20 laying near the ends of theellipsoid on its major axis. The periphery of the combustion chamber 26,labeled as the line 84 along the cylinder head mating surface 58, is notquite ovate; the periphery surrounding the intake valve seat 52 moreclosely approaches this valve seat than it does the exhaust valve seat54. This exposes a greater area on the cylinder head mating surface 58to the piston face reference surface 42, and thereby also helps tocreate more vigorous squish currents in the combustion chamber 26. Asbest shown in the views of the piston 34 in FIGS. 7-10, the top face 40of the piston is appropriately formed to match the periphery 84 of thecylinder head portion of the combustion chamber. The piston facereference surface 42 has at least one and preferably two widenedportions 42A. The beveled boundary surface 46 has at least one andpreferably two substantially straight portions 46A which extend from thewidened portions 42A of the piston face reference surface to the raisedpiston face surface 50. The two widened portions 42A of the pistonreference surface are preferably arranged to lie adjacent opposite sidesof one of the valve seats, e.g., adjacent to the beveled valve clearancesurfaces 48 for the exhaust valve, when the piston is at top deadcenter. The beveled boundary surface 46, including the substantiallystraight portions 46A, are bounded by the piston face reference surface42, which includes the widened portions 42A thereof. The beveledboundary surface 46, including the straight portions 46A as best shownin FIG. 7, and the beveled rim surface 28, including substantiallystraight portions 28A thereof as shown in FIG. 6, are formed to match,so that at top dead center the beveled boundary surface 46 of the pistonclosely approaches and is parallel to the beveled rim surface 28.

FIGS. 7 and 8 illustrate the piston 34 and particularly the piston topface 40. The raised face surface 50 is bounded by the beveled boundarysurface 46 and also by the beveled valve clearance surfaces 48. At topdead center, the raised face surface 50 closely approaches the chambershoulders 30A and 30B in the cylinder head 10 to produce the squishvolume 72 depicted in FIG. 4. Further, at top dead center, the beveledboundary surface 46 closely approaches the beveled rim surface 28, thebeveled valve clearance surfaces 48 closely approach the head 51 of theintake valve 14 and the head 53 of the exhaust valve 20, and the pistonface reference surface 42 closely approaches the cylinder head matingsurface 58, all creating squish currents.

Within standard IC engines, the area near the wall of the combustionchamber generally contains a higher concentration of unburnthydrocarbons during and after combustion due to the more quiescentboundary layer conditions adjacent to the chamber wall. Because thesquish currents within the invention greatly enhance the turbulencewithin the combustion chamber, the boundary layer is invaded by plumesof hot gases and reactive radicals during combustion, and greateramounts of unburnt hydrocarbons are consumed by the combustion process.This decreases the amount of unburnt hydrocarbons in the engine exhaust,and it also increases the fuel economy of the engine because lesseramounts of unburnt hydrocarbon chains escape the combustion chamberwithout contributing to the work output of the combustion process.

The cylinder head 10 and mating piston 34 may be provided together as akit and installed on existing engines to provide enhanced performance ofthe engine.

FIGS. 9 and 10 illustrates a piston 34 which is modified by the additionof a depression 74 in the piston face. The depression 74 increases thecombustion chamber volume (e.g., by 43.1 cc for the exemplary enginedimensions given above) and decreases the compression ratio to a levelmore appropriate for lower octane gasoline. An idealized schematicrepresentation of the combustion chamber with the piston depression 74is shown in FIG. 5. It is understood that the depression 74 in thepiston will generally have a flat bottom 88, as illustrated in FIGS. 9and 10, to ensure that the top wall of the piston under the depressionis of adequate thickness.

Raised vanes 90 and 91 as shown in FIG. 2 may be formed in the walls ofthe intake port 18 and exhaust port 24 adjacent the valve seats as shownin FIGS. 1 and 2 to enhance the flow of gases into and out of thecylinder. These vanes, which are preferably cast integrally with thehead, help to strengthen the floor of the intake and exhaust ports, inaddition to diverting gas flow around the intake and exhaust valves. Theenhanced flow of gases into and out of the combustion chamber furtherincreases the efficiency of the engine.

It is understood that the invention is not confined to the particularconstruction and arrangement of parts herein illustrated and described,but embraces such modified forms thereof as come within the scope of thefollowing claims.

What is claimed is:
 1. An internal combustion engine assemblycomprising:(a) a cylinder head having a cylinder head mating surface, acombustion chamber in the cylinder head recessed from the cylinder headmating surface, the combustion chamber including a wall defining adepression, a chamber shoulder, a beveled rim surface, an inlet valveseat and an exhaust valve seat in the wall of the depression, thedepression bounded around at least a part of its periphery by thechamber shoulder and the chamber shoulder being in turn bounded by thebeveled rim surface which extends from the periphery of the chambershoulder to the cylinder head mating surface; and (b) a cylinder blockincluding a cylinder block mating surface, a wall therein defining acylinder, and a piston within the cylinder, with the cylinder blockmating surface adjoining the cylinder head mating surface, the pistonhaving a piston top face including a piston face reference surface and araised piston face surface, with the piston face reference surfacelocated on the piston such that at top dead center it lies substantiallyin the plane of the cylinder block mating surface and closely approachesand is parallel to the cylinder head mating surface, the raised pistonface surface spaced from the piston face reference surface such that theraised piston face surface is above the cylinder head mating surfacewhen the piston is at top dead center, the piston top face furtherincluding a beveled boundary surface extending from the piston facereference surface to the raised face surface with the raised facesurface bounded by the beveled boundary surface, the piston facereference surface having at least one widened portion from which thebeveled boundary surface extends to the raised face surface, and whereinthe beveled boundary surface and the beveled rim surface are formed tomatch so that, at top dead center, the beveled boundary surface of thepiston closely approaches and is parallel to the beveled rim surface ofthe cylinder head, a portion of the raised piston face surface closelyapproaches and is parallel to the chamber shoulder, and the piston facereference surface including the widened portion thereof closelyapproaches and is parallel to the cylinder head mating surface.
 2. Theinternal combustion engine assembly of claim 1 wherein the raised pistonface surface is a planar surface over the area bounded by the beveledboundary surface.
 3. The internal combustion engine assembly of claim 1wherein the piston top face includes a wall defining a depressionextending downwardly from a planar portion of the raised piston facesurface towards the interior of the piston.
 4. The internal combustionengine assembly of claim 1 wherein at least one of the valve seatsoverlaps the chamber shoulder.
 5. The internal combustion engineassembly of claim 1 wherein at least one of the valve seats overlaps thechamber shoulder and the beveled rim surface, and the piston top faceincludes beveled valve clearance surfaces extending downwardly from aplanar raised piston face surface such that the beveled valve clearancesurfaces rest closely adjacent to valve heads seated in the valve seatswhen the piston reaches top dead center.
 6. The internal combustionengine assembly of claim 1 including a spark plug mounted in thedepression wall of the combustion chamber.
 7. The internal combustionengine assembly of claim 1 wherein the chamber shoulder has two parts,with a shoulder part on one side of the depression wider than theshoulder part on the opposite side of the depression.
 8. The internalcombustion engine assembly of claim 7 wherein the wider chamber shoulderis located on a side of the combustion chamber opposite to a spark plugmounted in the depression wall of the combustion chamber.
 9. Theinternal combustion engine assembly of claim 1 wherein the chambershoulder and beveled rim surface are formed in at least two partsarranged about the periphery of the depression.
 10. The internalcombustion engine assembly of claim 9 wherein the valve seats arelocated on the depression wall between the parts of the chamber shoulderand beveled rim surface.
 11. The internal combustion engine assembly ofclaim 1 wherein the beveled rim surface is formed in at least twoconnected parts, at least one of which is planar.
 12. The internalcombustion engine assembly of claim 11 wherein the planar part of thebeveled rim surface is adjacent to the exhaust valve seat.
 13. Theinternal combustion engine assembly of claim 1 wherein the depressionwall defines a substantially semiovoidal surface which has a major axis.14. The internal combustion engine assembly of claim 13 wherein theinlet and exhaust valve seats are located near the opposite sides of thedepression along the major axis.
 15. The internal combustion engineassembly of claim 14 wherein a spark plug is mounted in the wall of thedepression between the inlet and exhaust valve seats.
 16. The internalcombustion engine assembly of claim 1 wherein the intake valve seat islarger than the exhaust valve seat.
 17. The internal combustion engineassembly of claim 1 including an intake port in the cylinder headextending from the intake valve seat, and a vane integrally formed in awall of the intake port adjacent to the valve seat.
 18. The internalcombustion engine assembly of claim 1 including an exhaust port in thecylinder head extending from the exhaust valve seat, and a vaneintegrally formed in a wall of the exhaust port adjacent to the valveseat.
 19. A cylinder head and piston kit comprising:a cylinder headhaving a cylinder head mating surface, a combustion chamber in thecylinder head recessed from the cylinder head mating surface, thecombustion chamber including a wall defining a depression, a chambershoulder, a beveled rim surface, an inlet valve seat and an exhaustvalve seat in the wall of the depression, the depression bounded aroundat least a part of its periphery by the chamber shoulder and the chambershoulder being in turn bounded by the beveled rim surface which extendsfrom the periphery of the chamber shoulder to the cylinder head matingsurface; and a piston having a piston top face including a piston facereference surface and a raised piston face surface, with the piston facereference surface located on the piston such that when the piston isinstalled within an engine, at top dead center the piston face referencesurface closely approaches and is parallel to the cylinder head matingsurface, and with the raised piston face surface spaced from the pistonface reference surface such that the raised piston face surface is abovethe cylinder head mating surface when the piston is at top dead center,the piston top face further including a beveled boundary surfaceextending from the piston face reference surface to the raised facesurface with the raised face surface bounded by the beveled boundarysurface the piston face reference surface having at least one widenedportion from which the beveled boundary surface extends to the raisedface surface, and wherein the beveled boundary surface and the beveledrim surface are formed to match so that, at top dead center, the beveledboundary surface of the piston closely approaches and is parallel to thebeveled rim surface of the cylinder head, a portion of the raised pistonface surface closely approaches and is parallel to the chamber shoulder,and the piston face reference surface including the widened portionthereof closely approaches and is parallel to the cylinder head matingsurface.
 20. The cylinder head and piston kit of claim 19 wherein theraised piston face surface is a planar surface over the area bounded bythe beveled boundary surface.
 21. The cylinder head and piston kit ofclaim 19 wherein the piston top face includes a wall defining adepression extending downwardly from a planar portion of the raisedpiston face surface towards the interior of the piston.
 22. The cylinderhead and piston kit of claim 19 wherein at least one of the valve seatsoverlaps the chamber shoulder.
 23. The cylinder head and piston kit ofclaim 19 wherein at least one of the valve seats overlaps the chambershoulder and the beveled rim surface, and the piston top face includesbeveled valve clearance surfaces extending downwardly from a planarraised piston face surface such that the beveled valve clearancesurfaces rest closely adjacent to valve heads seated in the valve seatswhen the piston reaches top dead center.
 24. The cylinder head andpiston kit of claim 19 including a spark plug mounted in the depressionwall of the combustion chamber.
 25. The cylinder head and piston kit ofclaim 19 wherein the chamber shoulder has two parts, with a shoulderpart on one side of the depression wider than the shoulder part on theopposite side of the depression.
 26. The cylinder head and piston kit ofclaim 25 wherein the wider chamber shoulder is located on a side of thecombustion chamber opposite to a spark plug mounted in the depressionwall of the combustion chamber.
 27. The cylinder head and piston kit ofclaim 19 wherein the chamber shoulder and beveled rim surface are formedin at least two parts arranged about the periphery of the depression.28. The cylinder head and piston kit of claim 27 wherein the valve seatsare located on the depression wall between the parts of the chambershoulder and beveled rim surface.
 29. The cylinder head and piston kitof claim 19 wherein the beveled rim surface is formed in at least twoconnected parts, at least one of which is planar.
 30. The cylinder headand piston kit of claim 19 wherein the planar part of the beveled rimsurface is adjacent to the exhaust valve seat.
 31. The cylinder head andpiston kit of claim 19 wherein the depression wall defines asubstantially semiovoidal surface which has a major axis.
 32. Thecylinder head and piston kit of claim 31 wherein the inlet and exhaustvalve seats are located near the opposite sides of the depression alongthe major axis.
 33. The cylinder head and piston kit of claim 32 whereina spark plug is mounted in the wall of the depression between the inletand exhaust valve seats.
 34. The cylinder head and piston kit of claim19 wherein the intake valve seat is larger than the exhaust valve seat.35. The cylinder head and piston kit of claim 19 in combination with anintake valve and an exhaust valve.
 36. The cylinder head and piston kitof claim 19 including an intake port in the cylinder head extending fromthe intake valve seat, and a vane integrally formed in a wall of theintake port adjacent to the valve seat.
 37. The cylinder head and pistonkit of claim 19 including an exhaust port in the cylinder head extendingfrom the exhaust valve seat, and a vane integrally formed in a wall ofthe exhaust port adjacent to the valve seat.
 38. The internal combustionengine of claim 1 wherein the piston face reference surface has twowidened portions which are arranged to lie adjacent opposite sides ofone of the valve seats when the piston is at top dead center.
 39. Theinternal combustion engine of claim 1 wherein the beveled boundarysurface of the piston has a substantially straight portion thereofextending from at least one widened portion of the piston face referencesurface to the raised piston face surface.
 40. The internal combustionengine of claim 1 wherein the piston face reference surface has twowidened portions and the beveled boundary surface has two substantiallystraight portions thereof extending from the two widened portions to theraised piston face surface.
 41. The cylinder head and piston kit ofclaim 19 wherein the piston face reference surface has two widenedportions which are arranged to lie adjacent opposite sides of one of thevalve seats when the piston is installed in an engine and is at top deadcenter.
 42. The cylinder head and piston kit of claim 19 wherein thebeveled boundary surface of the piston has a substantially straightportion thereof extending from at least one widened portion of thepiston face reference surface to the raised pistion face surface. 43.The cylinder head and piston kit of claim 19 wherein the piston facereference surface has two widened portions and the beveled boundarysurface has two substantially straight portions thereof extending fromthe two widened portions to the raised piston face surface.